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Metabolic Syndrome

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Also known as: Syndrome X; Dysmetabolic Syndrome; Insulin Resistance Syndrome; Obesity Syndrome; Reaven Syndrome

What is metabolic syndrome?

Metabolic syndrome is a set of risk factors that increases a person's chance of developing serious conditions such as cardiovascular disease (CVD), type 2 diabetes, and stroke. These risk factors include:

Metabolic syndrome is a common condition that goes by many names (dysmetabolic syndrome, syndrome X, insulin resistance syndrome, obesity syndrome, and Reaven syndrome). Most people identified as having this syndrome have been educated about the importance of watching for signs of diabetes, having their blood pressure monitored and lipid levels checked, and exercising – but there has been little to tie all of these factors together except pursuit of a "healthier lifestyle."

The National Heart, Lung and Blood Institute (NHLBI) estimates that about 34% of Americans have metabolic syndrome. It can affect anyone at any age, but it is most frequently seen in people who are inactive and significantly overweight, with most of their excess fat in the abdominal area.

While several national and international organizations use certain criteria to define metabolic syndrome, others, including the American Diabetes Association (ADA), question the value of the specific diagnosis of metabolic syndrome. They point out that the criteria, taken together, are no more useful at predicting the risk of cardiovascular disease or diabetes than the individual criteria considered separately. The science needs to be clearer, suggests the ADA, before metabolic syndrome be considered a definable syndrome.

The World Health Organization (WHO) was the first to publish an internationally accepted definition for metabolic syndrome in 1998, but the criteria that have received the most widespread acceptance and use in the United States are those established in 2002 as guidelines in the third report of the National Cholesterol Education Program expert panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (ATP III).

In 2005, the American Heart Association (AHA) in conjunction with the NHLBI also released a scientific statement regarding metabolic syndrome that includes a set of criteria that defines the condition. In order to provide more consistency in both patient care and research, the International Diabetes Federation, NHLBI, AHA, World Heart Federation, and the International Association for the Study of Obesity published a joint statement in 2009 that describes a "harmonized" definition of metabolic syndrome. Waist circumference, with population and country-specific criteria, replaced obesity as a measure of body status.

The table below summarizes the four sets of criteria:

Criteria for Clinical Diagnosis of Metabolic Syndrome

Clinical MeasureWHO (1998)
AHA/NHLBI (2005)
Harmonization Definition (2005)
Criteria for diagnosis Insulin resistance plus two of the other criteria below Three of the criteria listed below Obesity as defined by waist circumference plus two of the other criteria below
Waist circumference (as the definition of obesity)   ≥40 inches (102 centimeters, cm) in men,
≥35 inches (88 cm) in women
≥37 inches (95 centimeters, cm) in men,
≥31 inches (80 cm) in women
Body mass index (BMI) BMI >30 kilograms/meter2    
Triglycerides ≥150 milligrams/deciliter (mg/dL) ≥150 milligrams/deciliter (mg/dL) ≥150 milligrams/deciliter (mg/dL)
HDL-C <35 mg/dL in men,
<39 mg/dL in women
<40 mg/dL in men,
<50 mg/dL in women or taking medication such as statins
<40 mg/dL in men,
<50 mg/dL in women or taking medication such as statins
Blood pressure ≥140/90 mm Hg Systolic ≥130 or diastolic 85 mm Hg or taking medication for high blood pressure Systolic ≥130 or diastolic ≥85 mm Hg or taking medication for high blood pressure
Glucose Impaired glucose tolerance, impaired fasting glucose or type 2 diabetes Fasting >100 mg/dL or taking medication for diabetes Fasting ≥100 mg/dL
Insulin resistance YES NO NO
Urine albumin (microalbuminuria) YES NO NO

Also frequently seen with metabolic syndrome are tendencies for excessive blood clotting and inflammation. While obvious symptoms may be absent, these features are a warning of an increased likelihood of clogged arteries, heart disease, stroke, diabetes, kidney disease, and even premature death. If left untreated, complications from diseases associated with untreated metabolic syndrome can develop in as few as 15 years. Those who have metabolic syndrome and also smoke tend to have an even poorer prognosis.

The root cause of most cases of metabolic syndrome can be traced back to poor eating habits and a sedentary lifestyle. In some cases, a diagnosis of metabolic syndrome has also been assigned to those already diagnosed with hypertension or with poorly controlled diabetes. There also seems to be an association with non-alcoholic fatty liver disease, polycystic ovarian disease, and some cancers. A few cases are thought to be linked to genetic factors.

All of the factors associated with metabolic syndrome are interrelated. Obesity and lack of exercise tend to lead to insulin resistance. Insulin resistance has a negative effect on lipid production, increasing VLDL (very low-density lipoprotein), LDL (low-density lipoprotein – the "bad" cholesterol), and triglyceride levels in the blood and decreasing HDL (high-density lipoprotein – the "good" cholesterol). This can lead to fatty plaque deposits in the arteries which, over time, can lead to cardiovascular disease and strokes. Insulin resistance also leads to increased insulin and glucose levels in the blood. Excess insulin increases sodium retention by the kidneys, which increases blood pressure and can lead to hypertension. Chronically elevated glucose levels in turn damage blood vessels and organs, such as the kidneys. [For more information, read Metabolic Syndrome: Additional Details.]

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